1. Field of the Invention
The present invention relates to a device and method of removing bubbles generated in molding glass fiber-reinforced plastic parts.
2. Background of the Related Art
Currently, a variety of parts made of glass fiber-reinforced plastic (hereinafter, referred to as “GFRP”) are manufactured, marketed and used. A typical example of such parts is a corrosion-resistant FRP pump which is used in a wide range of industrial fields, including semiconductor fabrication, chemical, waste water treatment, water purification, plating, drug manufacturing and textile industries.
Main parts of this corrosion-resistant FRP pump, such as an impeller, a casing and a shaft sleeve, are made of GFRP. However, these parts contain bubbles at large amounts (about 20% by volume). Such bubbles are disadvantageously liable to cause corrosion in the parts, and reduce the strength, thermal resistance and impact resistance of the parts, and also increase the thermal expansion and shrinkage of the parts. Thus, in order to maintain the corrosion resistance and durability of the parts at a given level, the content of the bubbles in the parts needs to be maintained at less than 5%.
Hereinafter, the cause and mechanism of generation of the bubbles will be concretely described.
Generally, a method of manufacturing the GFRP parts comprises the steps of placing glass fiber in a mold, impregnating the glass fiber with a resin and accelerator mixture and a curing agent, and repeating the step of applying glass fiber. When the resin and accelerator mixture is mixed with the curing agent, curing reaction occurs to generate volatile gas. If the gas is not sufficiently vented out, bubbles will remain in the GFRP parts.
Meanwhile, other bubbles generated in the GFRP parts include large bubbles caused by air or moisture trapped in the parts other than the gas, and small bubbles which remain on the interface between glass fiber and resin since the volatile gas is not removed. In addition, the bubbling is influenced by a molding method, or working conditions, such as temperature and humidity.
The bubbles contained in resin will determine the shrinkage of the resin, and become a factor of changing the surface characteristics and mechanical properties of the resin. Furthermore, the bubbles distributed on the surface and at the inside of the molded parts can reduce the mechanical properties of the parts, and upon the severe change of temperature, cause stress in the resin by shrinkage and expansion, thereby causing the deformation and fracture of the parts. Also, the bubbles have the greatest effect on the reduction of compression strength, transverse tensile strength, interlaminar shear strength and abrasion resistance, which vary depending on a matrix material, and also on the causing of thermal deformation.
Currently, molding of the GFRP parts for use in the FRP pump is conducted by hand working in view of working characteristics. Thus, if the GFRP parts contain bubbles therein, uniform quality will not be obtained even when the molding is conducted by one worker. Also, standardized precise property values of the GFRP parts for use in the corrosion-resistant FRP pump, such as corrosion resistance, strength, thermal resistance, impact resistance and durability, will not obtained.
Meanwhile, in order to remove bubbles, glass fibber may also be used in a powder form in molding the GFRP parts. In this case, however, there is a problem in that the mechanical properties of the glass fiber, such as tensile strength, compression strength, shear strength, abrasion resistance and thermal resistance, are greatly reduced such that the glass fiber does not sufficiently serve as reinforcement. In other words, in order to make the glass fiber act efficiently as reinforcement, the glass fiber must be used in a form cut to have the same size and shape as the parts without breaking or cutting it fine.